Analysis of the effect of temperature, pH, CO2 pressure and salinity on the olivine dissolution kinetics

AbstractThe dissolution kinetics of olivine has been extensively studied under several temperatures, CO2 pressures, and solution compositions. Dissolution is an important mechanism in the aqueous mineral carbonation process. The overall carbonation reaction consists of dissolution of mineral silicate, e.g. olivine, serpentine and wollastonite, followed by carbonate precipitation, thus fixing CO2 into naturally occurring stable solids, such as magnesite and calcite. The slowness of the dissolution kinetics hinders the overall carbonation reaction and in order to make the process technically and economically feasible, such a reaction should be sped up by finding the optimum operating conditions. Experiments were performed in a flow-through reactor at 90–120–150 ∘C. The pH was adjusted by adding either acids (e.g., HCl, citric acid) or LiOH, and by changing PCO2. The salinity was changed by adding NaCl and NaNO3. From the experimental data, the dissolution rate was estimated by using the population balance equation (PBE) model coupled with a mass balance, and the obtained values were regressed with a linear model log(r)=−npH−B, where r is the specific dissolution rate (mol s−1 cm−2)

Mineral carbonation process for CO2 sequestration

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Hoboken Groundwater Data

Data and Matlab code for plotting the data

Gas-solid carbonation kinetics of air pollution control residues for CO2 storage

Gas-solid carbonation of Air Pollution Control (APC) residues is a CO2 Capture and Storage (CCS) technology, where highly reactive Mg- or Ca-bearing materials adsorb CO2 and form stable Mg- or Ca-carbonates. The carbonation kinetics of this reaction have been studied at different temperatures, CO2 concentrations, and at atmospheric pressure in order to select the best operative conditions on the basis of CO2 stored and reaction time. The samples were initially heated up to the operative conditions under argon atmosphere and then carbonated under a CO2-argon atmosphere. All carbonation kinetics were characterized by a rapid chemically controlled reaction followed by a slower product layer diffusion-controlled process. Maximum conversions between 60% and 80% were achieved, depending on the operative temperature and CO2 concentration. Temperature did not notably affect the maximum conversion obtained in the experiments performed at temperatures equal or above 400 degrees C: the influence on the kinetics was masked by the change in initial composition due to dehydroxylation reaction and surface area while heating up to the operative temperature. A slight influence of CO2 concentration on the kinetics was observed, whereas no influence on the maximum conversion was noticed. The obtained results suggest that the flue gases with 10 vol.% CO2 concentration can be directly used to form stable carbonates, thus lumping capture and storage in a single step. The APC residues produced from the existing incineration plants would cover only 0.02-0.05% of the total CO2 European storage capacity required to comply with the Kyoto protocol objectives. Nevertheless, the proposed carbonation route could be applied to other residues, such as Cement Kiln Dust, Paper mill residues and Stainless Steel Desulphurization slags, characterized by a high content of free calcium oxides and hydroxides, thus increasing the impact of this process option. (C) 2008 Elsevier B.V. All rights reserved

Assessing exfiltration from an urban sewer by slug dosing a chemical tracer (NaCl)

Water resources in urban areas comprise both natural and man-made water bodies, including surface waters and groundwater. Groundwater aquifers can be recharged from several sources, some of which may transport high concentrations of organic and inorganic pollutants. Such sources include exfiltration from leaky sewer pipes that could pose a serious threat to groundwater quality because of large extent of urban drainage systems. When the shallow unconfined and confined aquifers are connected, the transport of organic and inorganic compounds and pathogenic organisms may cause serious pollution. Consequently, the deep confined groundwater aquifers could become polluted and their water would require advanced treatment if used as a source of drinking water. Several methods exist to evaluate the structural state of sewers. Some of these consist in direct surveying inside the sewer pipes (i.e., by closed circuit television, CCTV) and others in quantifying the exfiltration rates by the detection of wastewater markers in the groundwater [1]. The QUEST method [2] (QUantification of Exfiltration from Sewer with artificial Tracers) serves to assess directly the exfiltration from flowing sewers in dry weather. It is based on establishing a tracer mass balance for the investigated pipes. The solutions of a tracer (NaCl) are dosed in two manholes of the investigated reach, and at a downstream location, the conductivity of sewage is measured by in-line probes. The sources of errors affecting the exfiltration rate originate from the experimental results and data analysis. In particular, they are due to: flow rate, natural wastewater conductivity, shape of the tracer signals at the measuring point, transport of tracer and general disturbances in the sewer (caused for example by turbulence or solids). To minimise the errors in experiments and data analysis, preliminary measurements of flow rate, in-sewer background conductivity and tracer transport should be carried out. In the paper that follows, the results of application of the QUEST method to an urban sewer network in a suburban area of Rome and the importance of site-specific preliminary tests are presented